It is well known that cardiac arrhythmias may be controlled with devices such as implantable defibrillators. Past electrodes which deliver defibrillation therapy have been constructed of metal mesh adhered to a silicone rubber backing as disclosed in Heilman et al. in U.S. Pat. No. 4,291,707 or have been constructed of metal electrode coils adhesively bonded to a silicone rubber backing as disclosed in Holleman et al. in U.S. Pat. No. 4,971,070.
These electrodes have been manufactured using various techniques. In the case of the Heilman electrode, the electrode metal mesh is either stitched onto the rubber sheeting, or sandwiched between two layers of silicone rubber sheeting, one solid, and the other with open windows to allow for current distribution. The problem with these manufacturing processes is that the electrode is not firmly attached to the silicone rubber sheeting in all areas. Thus, tissue will have a tendency to grow into the electrode mesh and separate the electrode from the backing. If the need arises for explanting the electrode, complications arise due to the difficulty in separating the electrode from the ingrown tissue. In addition, the manufacturing methods are somewhat cumbersome to utilize.
In the case of the Holleman electrode, the electrode coils are adhesively bonded to the silicone sheeting, either with or without a central silicone core inserted into the coil. This technique involves an adhesive bonding step which must be carefully administered in order to ensure adequate bonding to all the surfaces. In addition, by using an adhesive, another material, which must be biocompatible, is added to the device thus complicating matters.
In U.S. Pat. No. 5,226,260 to Mar et al., a metal is completely embedded in silicone, using a molding operation; then, a jet of abrasive material is directed at the encapsulated metal to expose a portion of it to act as an electrode, leaving an unexposed portion firmly embedded in elastomeric material. The process of blasting the silicone surface layer with abrasive material to expose the metal is time consuming, difficult to control, and done by hand, making it very expensive. This is especially true when the metal of the electrode is of a complex geometry, having tiny coils or a mesh pattern, or when the thickness of silicone encapsulation varies as it usually does when compression molding is used to encapsulate coils.
It is therefore an object of the present invention to provide a method for manufacturing defibrillation electrodes using an automated material removal process.